Case-hardening process for articles of iron, steel, and steel alloys.



, TTED STATES PATEN FEDERICO GIOLITTI, OF TURIN, ITALY, ASSIGNOR T SOCIETA ANONIMA ITALIANA GIO. ANSALDO ARMSTRONG 85 (30., OF GENOA, ITALY.

CASE-HARDENING PROCESS FOR ARTICLES OF IRON, STEEL, AND STEEL ALLOYS.

No Drawing.

for Articles of Iron, Steel, and Steel Alloys,

of which the following is a specification.

This invention relates to the case hardening of objects of iron, steel or steel alloys.

' In former case hardening processes the objects to be treated were heated in contact with suitable solid or gaseous carbonizing substances and maintained for a part at least of the duration of the operation, out of contact with air.

The improved case hardening procem according to the present invention diflers from all former processesin that it consists in circulating a weak air current (under determined conditions of temperature, speed of flow, and the like) through the mass of granular carbon in -which the objects to.be case hardened are buried,the degree of concentration of carbon in the case hardened zones being regulated by adjusting the speed of the air current.

' It is impossible to state a prz'om' a general rule for the determination once for all of the speed of the air current necessary to obtain a determined concentration of carbon in the case hardened zone, because it is well known that the concentration be- I sides depending on this speed, is also afunction of the temperature, of the pressure and ofthe composition of the iron or steel under treatment, etc., so that it is impossible to give a rule covering an indefinite number of cases. It may however be aflirmed that in general the concentration of carbon in the case hardened zones is less when the speed of the air current which is caused to circulate through the mass of granular -carbon enveloping. the objects to betreated, is

,greater, but in every case it is necessary to make trial experiments in case hardening with currents of air of different speeds in order to determine the speed of current to be adopted in order to obtain a determined concentration of carbon inthe case hardened zones with the iron or steel of the given composition, operating at a given temperature for a determined 'period of time. These trials are easy to carry out and give resultswhich it is not difiicult to interpret, so that Specification of Letters Patent.

Application filed October 13, 1911.

Patented Sept. 30, 1913. Serial No. 654,518.

ternal surface of the objects bein treated,

there is obtained a case hardene zone in which concentration of carbon at the outer surface is about 0.82%.

2. Adopting the same conditions of temperature period, etc., but increasing the speed of the air current to the rate of twelve liters per hour per square decimeter of external surface of the steel objects being treated a concentration of carbon at the external surface of the hardened zone is "obtained not exceeding 0.55%.

- Having thus pointed out the principle upon which. is based my improved case hardening process, which principle as it is easy to see is totally different from the one upon which all hitherto known case hardening processes are based, there will now be described one of the numerous methods of carrying out the process. In this connection it may be stated that the improved process may be ap lied in different manners and with appliances which may vary according to the nature of the articles to be case hardened.

The objects to be case hardened are placed in a fixed or transportable container of sheet steel or refractory material, the form and dimensions of such container depending on those of the objects. Thus in many cases, as when case hardening small objects the ordinary retorts used in the preparation of i illuminating gas, are quite suitable.

The container, which I shall hereinafter refer to as a case hardening container, is placed inv a furnace by means of which it can be heated to a constant and uniform temperature between 900 and 1150 C. The container is provided wit-h a tightly closing door for the introduction of the objects to be case hardened, and with tubes arranged in such manner as to enable a weak air ourrent to-be circulated through the container;

A layer of carbon is first introduced into centimeters.

vwhich end is assisted by the case hardening containers, preferably wood charcoal heated to an elevated temperature and reduced to grains or small pieces, which carbon will be herein referred to as granular carbon. It is evident that the dimensions of the granular carbon and the thickness of the said layer thereof will vary with the dimensions, number and form of the objects to be case hardened. Assuming that there is to be case hardened at a single operation 100 kilograms of steel articles of not too complicated form (for example cones for ball bearings, springs for bicycle wheels or the like) each weighing not more than 400-500 grams, it will be suitable to pound the charcoal and utilize that portion which can pass through a sieve containing 25 meshes per square centimeter but which is retained by a sieve containing 81 meshes per square centimeter, the thickness of the layer of this granular carbon being about 10-15 On the other hand if the objects to be case hardened are very much larger, say armor plates for war vessels, the carbon should be used in much larger pieces and the thickness of the first layer increased to about 40-50 centimeters. The objects to be case hardened are laid on this layer of cement, spaces of about one or two centimeters being left between each object.

When the objects owing to their .form or weight tend to become embedded in the carbon it will be easy to keep them in place by resting them on apiece of wire gauze. If the objects are flat or elongated they can be arranged vertically. On the objects thus disposed there is scattered a quantity of granular carbon pr'epared as above described, suificient to completely cover them On this second layer of carbon the other ob-..

jects to be case hardened are arranged and covered with a further layer, this arrangement being repeated until the case hardening container is full.

The pure granular charcoal prepared in the above described manner and heated to an elevated temperature constitutes (es pecially when it has been. used several times for case hardening after the new process) a very mobile mass which packs with great facility into all the cavities of the objects, gently shaking the case hardening container/ 'It is obvious that it will be of great advantage to use charcoal in very small granules for case hardening objects of complicated form and having small cavities, a though .experiment has shown that with the present process the essential carbonizing agent is the gaseous mixture produced by the action of the air on the first layer of carbon, and the case hardening is effected also at these parts of the objects not in contact with the charcoal but even several centimeters away therefrom.

hydro-car As soon as the case hardening container has been filled the door is closed and a weak air current is caused to flow by means of the tubes before described. As already stated the speed of the air current depends upon the depth and nature of the casehardened zone which it is desired to obtain.

When the case hardening is finished the gaseous current is stopped and a door provided in the bottom of the container is opened. The granular carbon then flows out owing to its own weight and is collected in order to be afterward introduced into an other-case hardening container. The same charcoal may thus be used many times over, since only a very small quantity is consumed at the places where the air current enters the container. When the granular charcoal has been thus removed there remain in the container only the case hardened articles, which can be easily taken out and tempered or subjected to other treatment. lVhen the container has been emptied it is at once ready for a repetition of the process. cases, particularly when very deep zones of In many case hardening without high concentration of carbon are desired, it is preferable not to remove all .the' granular carbon from'the container but only a sufficient amount .to leave the surface of the articles uncovered, afterv which the heating and the circulation of air through the remaining carbon may be continued. \Vitlf this procedure there is obtained in the hardened zone an exceptionally uniform distribution of carbon, and the carbonizingmay penetrate to great depth, for example six or seven centimeters, without the concentration of carbon ever exceeding the value attained in the first part of the operation. r

The gases issuing from the case hardening container may be collected in a suitable gas vessel and utilized for subsequent circulation in the case hardening container. It is unnecessary therefore to burn a small quantity of granular carbon, which evidently occurs when air is directly utilized. The same result may be obtained from the beginning by passing the air through wood charcoal heated to 10001100 O. in a separate furnace before'allowing it to pass into the case hardening container.

If it is desired to have a higher degree-of concentration of carbon in the case hardened zone, this may be effected by introducing through suitably located tubes, larger or smaller uantities of gaseous or volatile ons, these latter being introduced in the region of the container in which the air arrives after havingpassed'; through a zone of granular carbon at meters in thickness. 7

,When it is desired to obtain very great uniformity of the case hardened zone over the whole surface of the articles, it is prefleast centierable to slowly rotate the case hardening container during the Operation. For the same purpose the articles, While still surrounded by the granular carbon, maybe fixed to a revolving metal shaft passing gas tight through the Wall of the case hardening container.

Having now described my invention What I claim as new and desire to secure by Letters Patent is 1. A process for case-hardening objects of iron, steel and steel alloys comprising the following steps; packing the objectsto be treated in granular carbon in a container, heating the container from an external source, passing a current of air through the carbon, and adjusting the rate of flow to obtain the desired concentration of carbon in the treated article; the temperature and duration of the treatment being kept con stant.

2. A process for case-hardening objects of iron, steel and steel alloys comprising the following steps; packing the objects to be treated 1n granular carbon in a container,

heating the container to 1000 C. from an external source, passing a current of air at about atmospheric pressure through the carbon and adjusting the rate of flow of the air to obtain the desired concentration of carbon in the treated article; thetemperature and duration. of the treatment being kept constant.

3. A process for case-hardening objects of iron, steel and steel alloys comprising the following steps; packing the objects to be treated in granular carbon, in a container, heating the container from an external source, passing a current of air and of a fluid hydrocarbon through the carbon, adjusting the rate of flow of theair and of the fluid hydrocarbon; to obtain the desired concentration of carbon in the treated article.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses. a

F EDERICO GIOLITTI. Vitnesses GHERAN, C. A. FERR RI. 

